The standard for screws is: product name (standard), material, strength grade, size and surface treatment.

1. In terms of product type, the torsion force of the outer hexagonal screw is relatively larger, the torque of the inner hexagonal screw is smaller, and the torque of the cross recess is smaller. In the product supporting use, it is generally recommended to use the screw level one level higher than the nut level, which is the most economical.

2, product material grade, here mainly talk about the carbon steel commonly used in screws, according to the level of carbon content, divided into: C1008 (corresponding to 4.8), C1035 (corresponding to 8.8), C1045 (corresponding to 10.9), SCM435 (corresponding to 12.9) Grade and 45H), the higher the carbon content, the harder the material. Screws of class 8.8 to above are all high-strength screws.

3. For specifications, such as M4x8, the outer diameter of the 4 finger tooth is 4mm, the effective length of the 8 finger embedded in the loaded object is 8mm, the general countersunk screw is loaded with the total length, and the half countersunk head screw is added with half head. length. The pan head screw cross does not include the head size.

4. When the same material is heat treated, the higher the hardness, the worse the toughness. Heat treatment is required for plating from grade 8.8 to above. There are two kinds of heat treatments currently performed: high-strength screws require heat treatment, that is, the hardness of screws from the inside to the outside is uniform; self-tapping screws require carburizing heat treatment, that is, the surface of the screws is impregnated with a layer of carbon, which is very hard. But the inside is very soft, if the carburization is inside, the screws will be burnt.

5, under normal circumstances, hardness > 32HRC, plating has the risk of hydrogen embrittlement. When hydrogen embrittlement is the product pickling (oily stain), H+ enters the inside of the metal to form bubbles, and the screw is used on the spot, and it breaks after 24 hours. Therefore, this product with a risk of hydrogen embrittlement needs to be dehydrogenated after electroplating.